1. Field of the Invention
This invention relates to mechanical door closers and holders. More specifically, this invention relates to a door closer and holder possessing an unusual ability to hold the door at a given degree of openness for a long period of time.
2. Discussion of the Prior Art
The prior art includes a number of patents which disclose door closers of the piston type wherein the piston is disposed in a chamber add is formed with a rack in an intermediate position thereof, driving a pinion attached to the closer arm. A spring urges the piston in a direction towards the closed position of the door.
An example of such a closer is found in the U.S. Pat. No. 4,378,612 which issued Apr. 5 1983 to Bruce N Beers. In this patent passageways are disposed in the wall of the closer and are occasionally obscured or opened by a portion of the piston as it moves in closing the door. The passageways are arranged so that, depending on the position of the piston, the fluid within the closer moves from one side of the piston to the other at the desired speed, the flow around the portion of the piston being determined by "sweep and latch" valves disposed in the passages.
One of the drawbacks of such prior structures is that with sweep and latch valve passageways extending directly into the wall of the piston chamber, it is not possible to have a good seal between the piston and the chamber itself. This is because if packing or other sealing means is disposed around the piston it engages the sharp edges defining the passage openings and may be actually sheared off from the rest of the packing and extruded through the control passages themselves. Because of such damage to packing by the openings in the wall of the piston chamber, packing has been dispensed with and the piston has been operated in the chamber without a seal, and there has been a gradual creeping of the piston toward the closed position as the oil moves along the periphery of it.
In the prior art there is a showing in a closer of using the pinion shaft of a closer to drive a cam linked to a switch for spreading flow in the closer at the latch end of the cycle. This showing, U.S. Pat. No. 4,267,619, issued May 19, 1981 to Suska, does not teach using such an arrangement to control hold open.